jlr3266 wrote:Jack shields have been used successfully all over. The problem was not the technology. LIRR also insisted that both mainline tracks could not come out together for bridging the area to allow cut and cover construction. The shield was the only remaining feasible option.

I agree that jack shields have been used successfully in the past and will be used successfully in the future. Their use here was a complete failure though, so unless the contractor was totally incompetent in the use of the technology (which I am not privvy about, but kind of doubt as it would have been bid out to a different more competent contractor by now), the failure speaks about whether the technology was appropriate for this specific tunnel or not. And the reality is that it was not appropriate for this tunnel. While I understand why LIRR was reluctant to have both tracks out at the same time, with proper planning this could have been built cut and cover over a week and have both tracks back on with slow speed restrictions while the concrete cures completely. I am guessing that now the plan is to take both tracks out only after ESA opens, so that the reduction in capacity to Penn is less of a problem, but I still do not see why this could not be done with a short closure.

In general, the MTA has become too concerned with complaints, both from the riding public and the politicos, to the point where necessary projects get way over budget in order to "minimize inconvenience" or get delayed again and again while looking for a "better" solution which might not even exist.

When the tunnel is awarded in a new contract, it will likely again be for a shield tunnel. You repeat the method was a failure while acknowledging that you know nothing about it. I already stated that the tunnel has been pushed out on the schedule since it does not serve any function for ESA service.

Your idea of taking the tracks out of service for a week, despite the fact that the LIRR refused to allow it for a weekend, is confusing. Why would the LIRR allow both tracks out of service after ESA is complete, if not now? It is not about reduced capacity. The original plan was to take the tracks out of service over several weekends and place them on steel framing so the tunnel could be constructed under the active tracks for the few months it takes to excavate, form, and place a concrete structure. LIRR did not want to risk both mainline tracks out of service if there are problems come Monday morning.

Building an entire tunnel by cut and cover in a week, and placing trains on curing concrete are not a thing.

If you have inside knowledge on the Westbound Bypass Tunnel and the planned future contracts, I defer to you, but ...

I did not mean to imply that they could pour the structure from concrete in place and let the trains on it. Most structures, even steel structures need some amount of concrete for their foundations. Apart from that everything else can be steel or precast elements put together like a puzzle in less than two days. The LIRR has already done that with the replacement of certain bridges on the Main Line. Normal concrete curing time is long. It achieves 80% of its final strength in 28 days. I am not aware of any critical infrastructure projects that have allowed the use of normal concrete as that means no use of the structure for those 28 days after its completion. With special additives the curing time can be cut by about a factor of 4 or down to a week or so. With proper overdesign and the fact that even special concrete is cheap by the standards of these projects, you could have a structure which has reached sufficient strength to carry a train in a week, especially if the only poured in place part are the foundations.

jlr3266 wrote:I already stated that the tunnel has been pushed out on the schedule since it does not serve any function for ESA service.

Of course it does not serve any function for ESA and ESA cannot take any more delays due to incompetence and mismanagement as it is already under pressure by the Feds and the Governor to deliver, so they prefer to stick it to the current LIRR to Penn and Amtrak by not eliminating the conflicting train moves at Harold for another 5 or so years until after ESA opens. This is the typical way bureaucracy works looking to minimize its own risk while sticking it to anyone else.

jlr3266 wrote: Why would the LIRR allow both tracks out of service after ESA is complete, if not now?

Because if something gets messed up and they cannot complete the work in the allocated time LIRR will have the option of rerouting some of the Penn Station bound trains into Grand Central. That option does not exist now.

Nobody waits 28 days for concrete to cure in the last few decades. Early strength concrete has been a thing for quite some time. We strip and use concrete in days, however the excavation, rebar and form placement, utility relocations, etc, are not assembled like a jig saw puzzle. Comparing a single span bridge in an open area to a few hundred feet of tunnel in Harold with minimal train interruption are comparing apples and rail fans.

If there is no will reasons will be found why something cannot be done, be it utility relocations (of course, this is done well in advance of the main work), lack of open space (of course, while still somewhat constrained if they had not been so set on building the west and east approaches to the tunnel first there would have been much more space to operate in) or something else. Leave it to a risk averse bureaucracy and a profit maximizing private enterprise to ensure that a project of moderate complexity blows up to take decades and hundreds of millions more than necessary. Indeed there are probably several bureaucracies involved (LIRR, MTACC, NYDOT, FRA, Amtrak, and I am probably forgetting some) each one trying to make a point that they are "important".

The failed Westbound Bypass contract itself is a microcosm of what is wrong with the way big projects are executed in the NY area. The operators (LIRR and Amtrak) are determined on practically zero tolerance for disruption of service excluding anything that is reasonable by the standards of everywhere else in the world. The MTACC and its contractors design and make decision on construction techniques even though they have never built anything using the said techniques (yeah, Cuomo is onto something with his design-build approach). The contract was awarded to the lowest bidder regardless of whether that bidder (Harold Structures Joint Venture (Schiavone/Picone JV)) had ever done anything like this before and then once the whole mess materialized, the MTA (but effectively the taxpayer) ended up paying extra and enduring mediocre service for those failures.

But back to the jacked shield. I am not aware of any other project where the MTACC has used this technique and I guarantee you that you will not see it used again for an MTA project for a very long time. Bureaucracies are risk averse and have long memories. While I am not a specialist in this field, the only other project in the US that I am aware to have used jacked shield is the Big Dig in Boston. There the winning bid included Skanska and Perini who leveraged extensively their relationships with UK firms which had completed many projects of this type before. As I said before, if this was just a case of incompetent contractor the contract would have been rebid already. If this could have been made to work, it would have been made to work. Schiavone gets enough work from the MTA that they are not keen on messing the relationship with one of their biggest customers for anything that was reasonably fixable. This was not salvageable. In a few years we will know what construction technique the MTA eventually decides to use, but I will bet you that it is not going to be a jacked shield. I have no insider information, but I do suspect that it will be some form of cut and cover, possibly with a temporary bypass track of some sort. By then with the construction of the third main track LIRR will be much more comfortable with short, a few days, type of closures due to the need to replace/install so many new undergrade bridges.